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Arseny Zinchenko
Arseny Zinchenko

Posted on • Originally published at rtfm.co.ua on

OpenVPN: Let’s Encrypt DNS verification on AWS Route53 and OpenVPN Access Server SSL certificate auto update

#openvpn #security #ssl #dns

In addition to the OpenVPN: SSL and hostname configuration post about OpenVPN Access Server, set up and configuration.

So, three months passed and it’s time to renew Let’s Encrypt SSL certificate (see. Prometheus: Alertmanager и blackbox-exporter — проверка срока действия SSL и нотификация в Slack, Rus).

I could use a well-know for me scheme with the webroot but OpenVPN AS accepts connections itself and there is no NGINX, and install it just for the webroot and Let’s Encrypt renewals – not too good idea.

Better let’s use DNS verification now.

AWS IAM and certbot-user

We have our domains served by AWS Route53 so use certbot-dns-route53 here.

Get your zone ID:

Create IAM-policy, in the ChangeResourceRecordSets set zone’s ID:

{
    "Version": "2012-10-17",
    "Id": "certbot-dns-route53 sample policy",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "route53:ListHostedZones",
                "route53:GetChange"
            ],
            "Resource": [
                "*"
            ]
        },
        {
            "Effect" : "Allow",
            "Action" : [
                "route53:ChangeResourceRecordSets"
            ],
            "Resource" : [
                "arn:aws:route53:::hostedzone/Z30***LB6"
            ]
        }
    ]
}
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(later I thought that it could be a good idea to add zone name to the policy or user names to make them more descriptive, as zone/user has access to the only one zone here)

Create a new user with the Programmatic access:

In the Permissions chose Attach existing policies directly and attach policy created above:

For testing – install aws-cli:

root@openvpnas2:~# apt -y install awscli
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Under the openvpnas user configure AWS CLI default-profile:

openvpnas@openvpnas2:~$ aws configure
AWS Access Key ID [None]: AKI***JEL
AWS Secret Access Key [None]: Lry***ide
Default region name [None]:
Default output format [None]: json
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Check config:

root@openvpnas2:~# cat /home/openvpnas/.aws/config
[default]
output = json
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OK – profile exists and it will be used later by the certbot.

To test access – try to get zones list:

openvpnas@openvpnas2:~$ aws route53 list-hosted-zones --output text
HOSTEDZONES     33C2D264-***-***-***-3052BEA607A9    /hostedzone/Z30***LB6      example.com. 103
...
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All good here.

certbot DNS verification

Install certbot:

openvpnas@openvpnas2:~$ sudo apt -y install certbot
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And the Route53 plugin:

openvpnas@openvpnas2:~$ sudo apt -y install python3-certbot-dns-route53
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Authorize and obtain the certificate:

root@openvpnas2:~# certbot certonly --dns-route53 -d vpn.example.com
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Found credentials in shared credentials file: ~/.aws/credentials
Plugins selected: Authenticator dns-route53, Installer None
Attempting to parse the version 0.31.0 renewal configuration file found at /etc/letsencrypt/renewal/vpn.example.com.conf with version 0.23.0 of Certbot. This might not work.
Cert is due for renewal, auto-renewing...
Renewing an existing certificate
Performing the following challenges:
dns-01 challenge for vpn.example.com
Waiting 10 seconds for DNS changes to propagate
Waiting for verification...
Cleaning up challenges

IMPORTANT NOTES:

- Congratulations! Your certificate and chain have been saved at:
/etc/letsencrypt/live/vpn.example.com/fullchain.pem
Your key file has been saved at:
/etc/letsencrypt/live/vpn.example.com/privkey.pem
...
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Check the zone in the Route53 – certbot must create a TXT-record here which will be used for authorization, and certbot will update it with a new value on each renewal

Check renewals config for this domain:

root@openvpnas2:~# cat /etc/letsencrypt/renewal/vpn.example.com.conf
renew_before_expiry = 30 days
...
Options used in the renewal process
[renewalparams]
authenticator = dns-route53
account = 6bc***4f6
installer = None
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Then will be enough just to execute certbot renew.

OpenVPN Access Server SSL update

To update SSL in the OpenVPN AS need to:

  1. upload the domain's certificate: sacli --key "cs.cert" --value_file "/etc/letsencrypt/live/vpn.example.com/cert.pem" ConfigPut
  2. upload Let’s Encrypt's certificate: sacli --key "cs.ca_bundle" --value_file "/etc/letsencrypt/live/vpn.example.com/chain.pem" ConfigPut
  3. upload our private key: sacli --key "cs.priv_key" --value_file "/etc/letsencrypt/live/vpn.example.com/privkey.pem" ConfigPut
  4. and rstart OpenVPN server

Collect all of them in one bash-script which will be called later by cron.

Go to the OpenVPN scripts catalog:

root@openvpnas2:~# cd  /usr/local/openvpn_as/scripts/
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Create a ssl_renew.sh script:

#!/usr/bin/env bash

SCRIPTS="/usr/local/openvpn_as/scripts/"

$SCRIPTS/sacli --key "cs.cert" --value_file "/etc/letsencrypt/live/vpn.example.com/cert.pem" ConfigPut
$SCRIPTS/sacli --key "cs.ca_bundle" --value_file "/etc/letsencrypt/live/vpn.example.com/chain.pem" ConfigPut
$SCRIPTS/sacli --key "cs.priv_key" --value_file "/etc/letsencrypt/live/vpn.example.com/privkey.pem" ConfigPut

$SCRIPTS/sacli start
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Just in case – backup exisitng keys:

root@openvpnas2:/usr/local/openvpn_as/scripts# cp /usr/local/openvpn_as/etc/web-ssl/server.crt /usr/local/openvpn_as/etc/web-ssl/server.crt.OLD

root@openvpnas2:/usr/local/openvpn_as/scripts# cp /usr/local/openvpn_as/etc/web-ssl/server.key /usr/local/openvpn_as/etc/web-ssl/server.key.OLD
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Run your new script:

root@openvpnas2:/usr/local/openvpn_as/scripts# ./ssl_renew.sh
[True, {}]
[True, {}]
[True, {}]
RunStart warm None
{
  "active_profile": "ProfileName",
  "errors": {},
  "service_status": {
    ...
    "web": "restarted"
  }
}

WILL_RESTART ['web', 'client']
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Check in a browser:

Then add a hook for certbot to run this script after renew.

Edit the /etc/letsencrypt/renewal/vpn.example.com.conf file:

...
[renewalparams]
authenticator = dns-route53
account = 6bc***4f6
installer = None
renew_hook = /usr/local/sbin/openvpnas_renewcerts.sh
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And the last thing – add a crontask with certbot renew, execute crontab -e:

0 0 * * * /usr/bin/certbot renew &> /var/log/letsencrypt/letsencrypt.log
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Done.

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dineshrathee12 profile image
Dinesh Rathee •

LetsEncrypt have revoked around 3 million certs last night due to a bug that they found. Are you impacted by this, Check out ?

DevTo
[+] dev.to/dineshrathee12/letsencrypt-...

GitHub
[+] github.com/dineshrathee12/Let-s-En...

LetsEncryptCommunity
[+] community.letsencrypt.org/t/letsen...

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